Apparatus for the forming and aging of titanium alloys



Feb, W65 R. E. JOHNSON ETAL mwm APPARATUS FOR THE FORMING AND AGING OF TITANIUM ALLOYS Filed Dec. 23, 1960 15 11 5 1 4 h he, Wm M u n. b F 1TH? 1 1T Ev W1 INVENTOR. ROBERT E. J OHNSOM RUSH MZD J. MCLINTI CK TORNEY States The present invention relates generally to the treatment of metals and more particularly, to an apparatus and method for simultaneously forming and aging titanium alloys.

Recent developments in the field of aircraft and missile propulsion have necessitated the use of materials'in airframes which are capable of withstanding the high temperatures and stresses generated during prolonged flights at speeds of Mach 2 and above. Airframe designers are in general agreement that titanium alloys offer numerous advantages over other materials available for this application. However", certain problems are encountered in working with titanium, not the least of which is the difiiculty in forming it into usable parts. Titanium alloy raw stock is normally purchased from the manufacturer in the solution heat-treated condition. However, finished titanium alloy parts, in order to be used in aircraft and missile structures, must generally bein the thermally stable, aged condition to achieve the required strength and temperature characteristics. While titanium alloy in the heat-treated condition at room temperature has exceptionally high strength, it is even stronger in the aged condition, and accordingly very difficult to form. To overcome this and other difliculties, titanium alloy parts are presently fhrmed in the'heat-treated condition and are aged after forming.

Thus, .it has generally been the practice to form the titanium alloy workpiece over a die to the desired shape, and'to remove the part from the die and to place it in a fixture which constrains'thepart in its formed'fc'onfiguration. The workpiece and fixture are then positioned within a'furnace and the workpiece is aged at an elevated temperaturefor a period'of from 6 to 20 hours, the time being dependent upon the particular alloy employed. There are several disadvantages in the above, currently employed, method, Experience has shown that it is'ex tremely difiicult to maintain the shape'of the workpiece during the aging cycle. Fabrication of the fixtures constitutes a large initial expense; and because of the high temperatures to which suchfixtures are almost continually 3,.l69,l56 Patented eh. 9, 1965 A further object is to provide apparatus and method for simultaneously forming and aging titanium alloy parts which permits a high production rate thereof.

Yet another object resides in the provision of an apparatus and method for forming and aging titanium alloy parts which is simple and inexpensive to practice.

These and other objects and advantages of the present invention will be more apparent to those skilled in the art from the following description of the appended drawing wherein:

FIGURE 1 is a perspective view of the apparatus of the invention with the forming boom shown in a terminal or forming position; and

FIGURE 2 is a vertical cross-sectional view of the die shown in FIGURE 1.

Referring now to FIGURE 1 of the drawing, the workpiece 10, which, for example, is a curved stiffener having the well known hat-section profile, is shown stretched over die 11, the constructional features of which will be described in conjunction with FIGURE 2. The die is securely fastened by means of bolts 12 extending through i the horizontal members of C-shaped clamping devices 13,

exposed, they require considerable maintenance and re-' work. Since the total time involved in the forming and aging operation varies from a minimum of Shows to a maximum of 24 hours, the'production-rate'is quite low.

" channel' of part 10. The purposeof the boom 30 and I The subject invention comprises a methodand apparatus for simultaneouslyforming and aging a titanium alloy part wherein such part is formed over a die and is aged by maintaining the part contiguous'with the die for a predetermined time while the latter is maintained at an elevated temperature. The part isthen in'the thermally st-able, aged condition, with strength characteristics equal both forming and-aging titanium alloy parts. 1 v Another object of the invention is to provide'a method 7 for simultaneously forming and aging-titanium alloy parts,

"provide'an apparatus which is particularly adapted for of the work table between the arms of clevis 20 on upright supporting structure 21, so asvto swing ina horizonal arc. To tlielower portion of the boom, is attached another hydraulic actuator 22. The ram 24 of this actuator is also fitted with a jaw25 whichfserves to grip the other end of the part. Themotion and'position of the boom 19 is effected by means of a'pair of hydraulioactuators 2'6 disposed above the boom and at tached at their inner ends to the supporting structure 21, a'sat 2:7, and at their outer ends to the boom through an upwardextension29 thereof.

A second and smaller boom 39, only a portion of which is shown'in'FlG-URE 1, is pivoted at its inner end to the upright supporting structure 21, asjati3ll, for movement independently of boom 19. At its outer end boom 30 i's'provided' with a depending extension 34, which at its lower extremity is bifurcated and carfies thereat a roller .;35."'T he boom 30 is adapted to rotate in a horizontal are such that roller 'is caused to track centrally of the roller 35, as will be more fully explained in the descrippart constant during the forming and aging operation,

a conventional temperature monitor unit 36 is employed. Thermocouples 37 inserted in the die sense the temperature thereof. Such information is transmitted to the monitor through thermocouple leads 38. The '.monitor 36 is, in turn, connected through wires 39 to a solenoid .Valve, the operation of which "will be explained in conjunction with FIGUREZ. Rotatable control dials and 51 respectively serve in conventional fashion as means for controlling the temperature'of the die and for maintaining the die at the selectedtemperature for the desired period of time, as hereinafter-more particularly indicated; Referring now to FIGURE2, the die 11 employed ,for this particular stiffener consists of ,a solid block of high temperature metaL-such as HR-l Meehanite, in the front face of which is formed a groove 41 having the crosssectional profile desired for the finished part and adapted for reception thereof, as illustrated. Above and below the die are positioned gas burner manifolds 42 which are areuately shaped to conform generally with the die curvature and which have a plurality of spaced openings 44 therealong. Such openings are directed toward the opposed upper and lower faces of the blocks so that the flames which emanate therefrom produce maximum heating in the block and consequently in the part received in face groove 41. Disposed about the manifolds are covers 45 shaped to conform generally to the die curvature. Such covers direct the heat from openings 44 into the block, prevent contamination of the workpiece by the burner flames, and contain the flames for purposes of safety. Gas is supplied to the manifolds through pipes 46, which are connected to a main gas pipe 47 which, in turn, is connected to a pressurized gas source. Positioned in the main pipe 47 between the source and the pipes 46 is the solenoid valve 48, referred to above. The monitor unit operates the solenoid such that when the temperature of the die is below that set on the control dial 50, the valve remains open, thus allowing gas to flow to the burners; and, when the temperature exceeds that desired, the valve closes, shutting off the gas supply. The timer (not shown) of conventional design is controllably connected with dial 51 to govern energization of the solenoid circuit and to determine the duration of die heating. Provided within each of the covers is a pilot light (not shown) for initiating combustion of the gas.

Inpractice, the process of this invention has been found particularly etfective in the forming and aging of two well known titanium alloys: titanium alloy RS 140, commercially available from Republic Steel Corporation, containing, by weight, aluminum, 2.75% chromium, 1.25% iron, and the balance titanium; and 4-3-1 titanium alloy, commercially available from: Titanium Metals Corporation of America, and containing by weight, 4%

aluminum, 3% molybdenum, and 1% vanadium. For

purposesof initial illustration, the apparatus and process will be operatively described in conjunction with a workpiece 10. comprised of the RS440 titanium alloy illustratively formed into an arcuate, elongate, stifiener. Such workpiece is first cut to size from a fiat piece of sheet stock.- It is then rough formed on a conventional brake press to assume an elongate straight configuration 'charofthe die at its terminal edge. Next, the boom 19 is' rotated into alignment with actuator 15, i.e., 90 degrees in a-counterclockwise direction, when viewed from above, 1

from the position of FIGURE 1; and the opposite end of the workpiece 10 issecured within jaw 25 of actuator 22., Theboom 19 is then rotated 90 degrees in the'opposite direction to reassume the position of FIGURE 1 so or slightly exceeds, tang'ency with the curvature of the die at the adjacent edge thereof. The die and workpiece are then heated to a predetermined temperature which, for the illustrative RS440 titanium alloy workpiece, is 1000 F. In this connection it should be noted that a considerable period of time is involved in heating the die to the forming and aging temperature. It may there fore be desirable, particularly in production runs, to maintain the die at such temperature intermediate the forming of different parts. The workpiece is then stretched over the heated die by means of the actuators 15 and 22 which effect outward movement of jaws 17 and 25. In order to assure proper formation of the hat-section profile, the boomfit) is rotated one or more times around the workpiece, the roller 35 tracking in-the workpiece channel, thereby forcing the material into conformitywith the die. .The tension on the workpiece is sustained for as tobend the workpiece around the die until it achieves,

approximately 10 minutes after initial application. The aging temperature, also 1000 F. for the illustrative workpiece, is maintained for from 5 to 10 minutes after the tension is relaxed. The 1000 F. temperature is thus maintained for a total period of from 15 to 20 minutes. Although a period of 15 to 20 minutes is preferred, it has been found that a period of from 10 to 30 minutes is satisfactory. By thus heating the die to 1000 F., the possibility of spring back of the formed part is effectively prevented.

After completion of aging, the part is'removed from the stretching machine and die, and is trimmed to size and cleaned of the purplish oxidation product which usually forms on the part. Such cleaning may be elfected by immersing the part in an alkaline cleaning solution, such as aqueous sodium hydroxide, for from 15 to 45 minutes followed by a hydrofluoric-nitric acid bath at room temperature for from 2 to 5 minutes, and a subsequent rinse in tap water.

The 1000 F. temperature utilized both during forming and aging of the above RS-140 alloy is 100 F. above the temperature normally used in the aging of such alloy. By thus increasing the aging temperature and acconn plishing aging at the same time as forming, there is eliminated the separate aging step, which for RS-140 alloy requires, under conventional practice, a period of 6 hours, in addition to the time involved in-the forming operation; and importantly, it has been found that, notwithstanding the extreme reduction in aging time thus effected, the final part in its thermally stable, aged condition, has strength characteristics substantially equivalent to similarly constituted parts aged in. conventional fashion.

As above indicated, the apparatus and process of this invention have also been employed in the forming of 4-3-1 titanium alloy, with excellent results. The forming and aging operations are accomplished in the manner above described. However, the temperatures and the aging periods employed are different. It has been found that a temperature of 1100 F. is required for aging 43l titanium alloy and that when this material is formed and aged at such temperature with an aggregate aging time of from 10 to 20 minutes, excellent results with noformed part spring back, are obtained. Satisfactory results have also been obtained when the parthas been maintained contiguous with the heated die for aperiod of from 5 to 30 minutes. Thereduction of aging time in the case f of the 4-3.1 alloy iseven greater than that achieved in processing RS440, inasmuch as thenormal aging temperature for 4-3 1 titanium alloy is 12 hours, over and above thetime involved in itsforrning. i

It is, of course, apparent that the stiffener, with respect to Which the invention has beendescribed, is but one of many parts'which the present invention is capable of forming and aging. Various othertitanium parts may be formed and agedby means of the apparatus and method of this invention,-including skins which involve either simple or compound curvature. In most instances it is desirable to employ some means, such as the roller in the embodiment illustrated, for forcing the workpiece against the die. However, with parts having only slight curvature which are stretch-formed, such means may usually be eliminated.

Although I have described and illustrated the preferred embodiment of the invention with respect to stretch forming, it will be understood thatthe invention is not limited thereto nor to the specific construction and operation thus of a metal workpiece comprising, in combination, a die of desired configuration having a pair of generally opposed heat receiving faces between whose corresponding edge margins extends a shaped forming face, means for forming said workpiece by forcing same against said die forming face and for maintaining said workpiece thereagainst, means for heating said die and the workpiece positioned thereagainst including a pair of manifold members each having at least one burner opening therein, said burner-openings being disposed to direct flame at said opposed faces of said die and means for confining said flames to prevent contamination ofthe workpiece, and means for controlling the heating of said die by said heating means and thereby the temperature of the workpiece held against said die forming face.

2. Apparatus for the simultaneous forming and aging of a metal workpiece comprising, in combination, a die having a forming face and a pair of generally opposed heat receiving faces extending from the margins thereof, means for forming said workpiece by forcing same against said forming face and for maintaining the'workpiece thereagainst, means for heating said die and the workpiece p'ositioned thereagainst including manifold members each having at least one burner opening therein disposed adjacent said heat receiving die faces for directing flame thereat and covering means for confining said flame to prevent contamination of the workpiece, and means for controlling the temperature of said die and the temperature of said workpiece while same is positioned against said die forming face.

3. The combination of claim 2, wherein is included means for controlling the period of time during which said die is heated by said heating means.

4. Apparatus for the simultaneous forming and aging of a metal workpiece comprising, in combination, a die having a forming face and a pair of opposed heat receiving faces bounding said forming face, means for forming said workpiece by forcing same againstsaid die forming face and for maintaining the workpiece thereagainst, means for rollably abutting said workpiece while same is positioned against said die forming face' thereby to assist in the forming of the workpiece, means for heating said die forming face by applying heat to said heat receiving faces, and means for controlling the temperature of said die and the temperature of said workpiece held thereagainst.

5. Apparatus for the simultaneous forming and aging of a metal workpiece comprising, in combination, a die of generally rectangular cross section having a forming face and extending from either margin thereof in substantially parallel relationship a pair of heat receiving faces, means for gripping either end of said workpiece and stretching same into contiguous relationship with said forming face of said die, means for rollably abutting said workpiece while same is stretched contiguous with said die thereby to assist in the forming of the workpiece, heating means including a pair of manifold members having burner openings oriented to direct flame at said heat receiving faces, covers enclosing said manifold members to shield said burner openings and prevent contamination of said workpiece by said heating means, and means for controlling the heating of said die by said heating means and thereby the temperature of said workpiece positioned against the die by said stretching means.

6. The combination of claim 5, wherein means are provided for controlling the period of time during Which said die is heated by said heating means.

References Cited by the Examiner UNITED STATES PATENTS 1,877,629 9/32 Replogle.

2,527,983 10/50 Brown et al 148-12.7

2,762,734 9/56 Corral l4812.7

2,905,225 9/59 Lalli 153-32 2,920,676 l/ Turnblade 153-32 .MORRIS O. WOLK, Primary Examiner.

RAY K. WINDHAM, JAMES H. TAYMAN, IR.,

Examiners. 

1. APPARATUS FOR THE SIMULTANEOUS FORMING AND AGING OF A METAL WORKPIECE COMPRISING, IN COMBINATION, A DIE OF DESIRED CONFIGURATION HAVING A PAIR OF GENERALLY OPPOSED HEAT RECEIVING FACES BETWEEN WHOSE CORRESPONDING EDGE MARGINS EXTENDS A SHAPED FORMING FACE, MEANS FOR FORMING SAID WORKPIECE BY FORCING SAME AGSINST SAID DIE FORMING FACE AND FOR MAINTAINING SAID WORKPIECE THEREAGAINST, MEANS FOR HEATING SAID DIE AND THE WORKPIECE POSITIONED THEREAGAINST INCLUDING A PAIR OF MANIFOLD MEMBERS EACH HAVING AT LEAST ONE BURNER OPENING THEREIN, SAID BURNER OPENING BEING DISPOSED TO DIRECT FLAME AT SAID OPPOSED FACE OF SAID DIE AND MEANS FOR CONFINING SAID FLAMES TO PREVENT CONTAMINATION OF THE WORKPIECE, AND MEANS FOR CONTROLLING THE HEATING OF SAID DIE BY SAID HEATING MEANS AND THEREBY THE TEMPERATURE OF THE WORKPIECE HELD AGAINST SAID DIE FORMING FACE. 